A conveniently portable archery device and a method for calibrating the center shot of a bow using the outer sidewall of a riser as a reference point, and without requiring attachment of the device to the bow. The device may easily and quickly allow the transverse position of the bow string to be marked, and also allow the position of the arrow rest to be adjusted so that an arrow may be correctly centered along its length with respect to the bowstring for more accurate firing. In one embodiment, the device is an improvement of a bow square article that in addition to being used to measure the nock point and brace height, equalize the tiller distances, and measure the peep sight, may also assist in calibrating center shot.